Java 线程 ArrayIndexOutOfBoundsException

Question

这个问题已经有答案了:

What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it? (25 个回答)

已关闭 1 年前。

我用线程编写了一个程序(用于自学)，它使用 2 个线程计算数组元素的乘法。但我为两个线程都得到了 ArrayIndexOutOfBoundsException 。错误看起来像这样:

Exception in thread "Thread-1" Exception in thread "Thread-0" Executing multiplying of last2elements
          java.lang.ArrayIndexOutOfBoundsException: 1
          at FirstPart.run(FirstPart.java:12)
          java.lang.ArrayIndexOutOfBoundsException: 1
          at SecondPart.run(SecondPart.java:10)

Java 代码:

FirstPart.java

public class FirstPart extends Thread {
    int multiply = 1;
    static int n;
    static int[] v = new int[n];

    public void run() {
        System.out.println("Executing multiplying of first "+MultiplyDemo.cap1+"elements"); 
        for(int i = 1; i <= MultiplyDemo.cap1; i++) {
            multiply = multiply * FirstPart.v[i];
            System.out.println("Multiplication is "+ multiply);
        }

    }
}

SecondPart.java:

public class SecondPart extends Thread {
    int multiply = 1;

    public void run() {
        System.out.println("Executing multiplying of last " + (FirstPart.n - MultiplyDemo.cap1) + "elements"); 

        for(int i = MultiplyDemo.cap1;i <= FirstPart.n; i++) {
            multiply=multiply*FirstPart.v[i];
            System.out.println("Multiplication is "+multiply);
        }
    }
}

MultiplyDemo.java:

import java.util.Scanner;
import java.util.Vector;


public class MultiplyDemo {

    public static int cap1;


    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.println("introduceti numarul de elemente din vector:");
        FirstPart.n=s.nextInt();

        int []v=new int[FirstPart.n];
        System.out.println("Elementele vectorului sunt");
        for(int i = 0; i < v.length; i++)
            v[i]=s.nextInt();         
        cap1=FirstPart.n / 2;

        FirstPart thread1=new FirstPart();
        SecondPart thread2=new SecondPart();

        thread1.start();
        thread2.start();

        try { // wait for completion of all thread and then sum
            thread1.join();
            thread2.join(); //wait for completion of MathCos object 
            double z = thread1.multiply + thread2.multiply;
            System.out.println("produsul elementelor este" +z);
        } 
        catch(InterruptedException IntExp) {
        }

    }
}

Answer 1

数组索引从 0 开始；如果数组的大小为 n有效索引的范围为 0..n-1 .
你所有的for使用 <= 进行循环检查而不是使用<这就是为什么你得到 ArrayIndexOutOfBoundsException .

通常数组上的“for 循环”具有以下形式:

Object[] array = new Object[size];
for(int i = 0;i < array.length;i++) {
  ..
}

这样你就永远不会超过数组的大小